1. Field of the Invention
The present invention relates to a semiconductor device, and particularly to a power semiconductor device.
2. Description of the Background Art
A vertical-type semiconductor device is a type of power semiconductor device. In the vertical-type semiconductor device, electric current is conducted (ON state) or interrupted (OFF state) between a front surface side and a rear surface side of the semiconductor device. On the front surface side of the semiconductor substrate, for example, a region is formed in which a switching element such as IGBT (Insulated Gate Bipolar Transistor) and the like are arranged. In this region, main current flows when the semiconductor device is electrically conductive, and this region is called active region.
In the case where the semiconductor device is a power device for which a high breakdown voltage is required, the front surface side of a semiconductor substrate includes the active region formed as a central region and a termination structure portion formed to surround the active region. The termination structure portion is structured to include a breakdown voltage layer for maintaining a breakdown voltage characteristic of the semiconductor device. As such a termination structure portion, a guard ring structure including a guard ring region or a RESURF (REduced SURface Field) structure including a RESURF layer, for example, is applied.
In the semiconductor device, for the purpose of protecting the active region and the termination structure portion from the external environment, an electrically-insulating protective film is formed to generally cover these active region and termination structure portion. As the protective film, an insulating film such as silicon oxide or silicon nitride for example is used. A resin-based material may also be used. Further, a protective film made up of a plurality of materials in the shape of layers may also be formed depending on the case.
In a process such as packaging of the semiconductor device, charge may be externally introduced onto the protective film in some cases. The introduced charge may cause local field crowding, leading to non-uniform field distribution. Due to this, the resultant breakdown voltage is lower than an expected breakdown voltage, and a problem arises that a breakdown voltage characteristic cannot be ensured. In order to solve this problem, PTL 1 (Japanese Patent Laying-Open No. 2008-103530) proposes a semiconductor device in which such an influence of the charge is reduced.